Hsueh-Hsiao Wang

Synthesis, Characterization, and Bioconjugation of Fluorescent Gold Nanoclusters toward Biological Labeling Applications

Synthesis of ultrasmall water-soluble fluorescent gold nanoclusters is reported. The clusters have a decent quantum yield, high colloidal stability, and can be readily conjugated with biological molecules. Specific staining of cells and nonspecific uptake by living cells is demonstrated.

Fluorescent Gold Nanoclusters as a Biocompatible Marker for In Vitro and In Vivo Tracking of Endothelial Cells

We have been investigating the fluorescent property and biocompatibility of novel fluorescent gold nanoclusters (FANC) in human aortic endothelial cells (HAEC) and endothelial progenitor cells (EPC). FANC (50-1000 nmol/L) was delivered into cells via the liposome complex. The fluorescence lasted for at least 28 days with a half-life of 9 days in vitro. Examination of 12 transcripts regulating the essential function of endothelial cells after a 72 h delivery showed that only the vascular cell adhesion molecule 1 and the vascular endothelial cadherin were down-regulated at high concentration (500 nmol/L). In addition, no activation of caspase 3 or proliferating cell nuclear antigens was detected. 3-[4,5-Dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide (MTT) assay demonstrated that, unlike the markedly suppressed viability in cells treated with quantum dots, FANC had minimal effect on the viability, unless above 500 nmol/L, at which level a minor reduction of viability mainly caused by liposome was found. Tube formation assay showed no impaired angiogenesis in the EPC treated with FANC. In vivo study using hindlimb ischemic mice with an intramuscular injection of FANC-labeled human EPC showed that the cells preserved an angiogenic potential and exhibited traceable signals after 21 days. These findings demonstrated that FANC is a promising biocompatible fluorescent probe.

Improvement of conversion efficiency for multi-junction solar cells by incorporation of Au nanoclusters.

We studied the photoluminescence (PL) and photovoltaic current-voltage characteristics of the three-junction InGaP/InGaAs/Ge solar cells by depositing Au nanoclusters on the cell surface. The increases of the PL intensity and short-circuit current after incorporation of Au nanoclusters are evident. An increase of 15.3% in energy conversion efficiency (from 19.6 to 22.6%) is obtained for the three-junction solar cells in which Au nanoclusters have been incorporated. We suggest that the increased light trapping due to radiative scattering from Au nanoclusters is responsible for improving the performance of the three-junction solar cells.

Reduction of connexin43 in human endothelial progenitor cells impairs the angiogenic potential

Our previous work showed that arsenic trioxide down-regulated Cx43 and attenuated the angiogenic potential of human late endothelial progenitor cells (EPC). However, the relation between Cx43 and angiogenic activity of the EPC remained unclear. In the study, human late EPC were treated with siRNA specific to Cx43 (Cx43siRNA). The expression profiles as well as activity of the treated cells were examined. In parallel, the angiogenic potential of human EPC treated with Cx43siRNA was evaluated using murine hind limb ischemic model. The results showed that, in the EPC treated with Cx43siRNA, the activity of migration, proliferation, and angiogenic potential were attenuated, accompanied by reduction in vascular endothelial growth factor (VEGF) expression. In hind limb ischemia mice, EPC treated with Cx43siRNA lost the therapeutic angiogenic potential. VEGF supplementation partially recovered the activity impaired by Cx43 down-regulation. In conclusion, reduced Cx43 expression per se in the EPC causes decreased expression of VEGF and impaired angiogenic potential of the cells. Prevention of Cx43 reduction is a potential target to maintain the angiogenic potential of the EPC.

Recombination dynamics of photoluminescence in thiol-protected gold nanoclusters

Recombination dynamics of photoluminescence (PL) in Au nanoclusters (NCs) with different capping molecules were studied with time-resolved PL. Based on the emission-energy of carrier lifetimes; we suggest that the fast and slow PL decay of Au NCs originates from recombination of the linear Au–S bond and the staple motif, respectively. The effect of carrier localization in Au NCs was found to depend on the capping molecules. The zero-dimensionality of carriers in Au NCs was demonstrated by the temperature dependence of the time-resolved PL.

Efficient energy transfer from InGaN quantum wells to Ag nanoparticles

Nonradiative energy transfer from an InGaN quantum well to Ag nanoparticles is unambiguously demonstrated by the time-resolved photoluminescence. The distance dependence of the energy transfer rate is found to be proportional to 1/d(3), in good agreement with the prediction of the dipole interaction calculated from the Joule losses in acceptors. The maximum energy-transfer efficiency of this energy transfer system can be as high as 83%.

Interrelation of transport and optical properties in gold nanoclusters

Temperature dependence of the electrical conductivity and photoluminescence (PL) in Au nanoclusters (NCs) is investigated. The correlation of the conductivity and PL in Au NCs at different temperatures is evident: (i) for T<50 K, both the conductivity and PL intensity decrease with temperature, which suggests thermal structural fluctuations; (ii) for 50 K<T<90 K, conductivity and PL are explained by variable range hopping; (iii) for 90 K<T<170 K, simple thermal activated hopping dominates in conductivity, with a rate-equation model proposed to analyze the carrier transfer in PL.Temperature dependence of the electrical conductivity and photoluminescence (PL) in Au nanoclusters (NCs) is investigated. The correlation of the conductivity and PL in Au NCs at different temperatures is evident: (i) for T<50 K, both the conductivity and PL intensity decrease with temperature, which suggests thermal structural fluctuations; (ii) for 50 K<T<90 K, conductivity and PL are explained by variable range hopping; (iii) for 90 K<T<170 K, simple thermal activated hopping dominates in conductivity, with a rate-equation model proposed to analyze the carrier transfer in PL.

Synthesis and surface modification of highly fluorescent gold nanoclusters and their exploitation for cellular labeling

We introduce a general approach to make colorful fluorescent gold nanoclusters which are protected by dihydrolipoic acid, mercaptoundecanoic acid and polyethylenimine. The fluorescent gold nanoclusters can perform a variety of bioconjugation processes such as PEGylation, biotinylation as well as forming complex nanobioconjugates with streptavidins. The brightening effects under proper surface modification are also reported. The clusters have a decent quantum yield, high colloidal stability, and can be readily conjugated with biological molecules. Nonspecific uptake by human aortic endothelial cells is demonstrated.

Dihydrolipoic Acid Induces Cytotoxicity in Mouse Blastocysts through Apoptosis Processes

α-Lipoic acid (LA) is a thiol with antioxidant properties that protects against oxidative stress-induced apoptosis. LA is absorbed from the diet, taken up by cells and tissues, and subsequently reduced to dihydrolipoic acid (DHLA). In view of the recent application of DHLA as a hydrophilic nanomaterial preparation, determination of its biosafety profile is essential. In the current study, we examined the cytotoxic effects of DHLA on mouse embryos at the blastocyst stage, subsequent embryonic attachment and outgrowth in vitro, in vivo implantation by embryo transfer, and early embryonic development in an animal model. Blastocysts treated with 50 μM DHLA exhibited significantly increased apoptosis and a corresponding decrease in total cell number. Notably, the implantation success rates of blastocysts pretreated with DHLA were lower than that of their control counterparts. Moreover, in vitro treatment with 50 μM DHLA was associated with increased resorption of post-implantation embryos and decreased fetal weight. Data obtained using an in vivo mouse model further disclosed that consumption of drinking water containing 100 μM DHLA led to decreased early embryo development, specifically, inhibition of development to the blastocyst stage. However, it appears that concentrations of DHLA lower than 50 μM do not exert a hazardous effect on embryonic development. Our results collectively indicate that in vitro and in vivo exposure to concentrations of DHLA higher than 50 μM DHLA induces apoptosis and retards early pre- and post-implantation development, and support the potential of DHLA to induce embryonic cytotoxicity.

Site-selective photoluminescence in thiol-capped gold nanoclusters

Photoluminescence (PL) from the thiol-capped Au nonoclusters (NCs) has been investigated under site-selective excitation. Upon scanning the excitation light with energy below 2.1 eV down to 1.6 eV, the PL narrows and begins shifting linearly with excitation energy. The time-resolved PL was studied and the PL decay traces of Au NCs were found to depend on the excitation and emission energies. The slow carrier relaxation in the localized states is suggested to be responsible for the line narrowing and peak-shift in the site-selective PL.